1. Technical Field
The present invention relates to rotors for rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators.
2. Description of Related Art
There are known rotors for rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators. Those rotors include a rotor core and a plurality of permanent magnets. The rotor core is configured to be disposed in radial opposition to a stator of the rotating electric machine. The rotor core has a plurality of pairs of magnet-receiving holes formed therein. Each pair of the magnet-receiving holes is arranged in a substantially V-shape that opens toward the stator side. Each of the permanent magnets is received in a corresponding one of the magnet-receiving holes of the rotor core. Further, for each pair of the magnet-receiving holes, the two corresponding permanent magnets which are respectively received in the two magnet-receiving holes of the pair are arranged so as to together form one magnetic pole of the rotor core.
Japanese Unexamined Patent Application Publication No. 2006-311730 (to be simply referred to as Patent Document 1 hereinafter) discloses a rotor for a rotating electric machine. In the rotor, each of the permanent magnets is arranged in the corresponding one of the magnet-receiving holes of the rotor core so that there is formed a gap between a radially-outer side surface of the permanent magnet and a wall surface of the corresponding magnet-receiving hole. The gap has a uniform width at a central portion in a width direction of the permanent magnet. Further, the gap has a greater width at end portions in the width direction of the permanent magnet than at the central portion. Consequently, with the above arrangement of the permanent magnets in the corresponding magnet-receiving holes of the rotor core, it is possible to prevent local stress concentration from occurring in the rotor core.
However, though Patent Document 1 discloses how to reduce stress concentration on a bridge connecting the permanent magnet and a q-axis core, it fails to disclose how to reduce stress concentration on a radially innermost portion of the corresponding magnet-receiving hole. The stress concentration on the radially innermost portion of the corresponding magnet-receiving hole occurs when the rotor core has a small cross-sectional area. In particular, when the rotor is used in a motor generator which has a gear or a large-diameter shaft provided radially inside of the rotor, the maximum stress induced in the radially innermost portion of the corresponding magnet-receiving hole is almost equal to that induced in the bridge. In addition, in the rotor disclosed in Patent Document 1, there is formed, at the radially innermost portion of the corresponding magnet-receiving hole, a protrusion for positioning the permanent magnet in the corresponding magnet-receiving hole. Consequently, due to the protrusion, a maximum thermal stress is also induced in the radially innermost portion of the corresponding magnet-receiving hole.